CVE-2026-44636 libsixel: integer overflow in encoder
An integer overflow in libsixel's encoder allows heap buffer overflows when processing large image dimensions, potentially leading to code execution or crashes.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-44636?
CVE-2026-44636 is a high-severity vulnerability in saitoha libsixel, published on 14 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. From to 1.8.7-r1, signed integer overflow in sixel_encode_highcolor's allocation size calculation can lead to a heap buffer overflow. The public sixel_encode entry point validates only that width and height are greater than zero, with no upper bound. width and height are multiplied as plain int when computing the allocation size for paletted_pixels and normalized_pixels. Any caller that asks libsixel to encode a pixel buffer with width times height greater than INT_MAX (about 2.15 billion) will hit a wrapped allocation size; under the right wrap, the malloc succeeds with a buffer much smaller than the encoder expects, and the encoder writes past the end of the heap allocation. This vulnerability is fixed in 1.8.7-r2.
Which versions are affected by CVE-2026-44636?
It affects 1 product.
Products include Saitoha Libsixel.
How do I fix CVE-2026-44636?
Upgrade to a fixed version.
Is CVE-2026-44636 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44636 exists.
Other vulnerabilities in saitoha libsixel
Sources
Also known as DEBIAN-CVE-2026-44636, GHSA-hx93-w8p2-ffh5, UBUNTU-CVE-2026-44636.